The present invention relates generally to a system including an arrangement for tracking the positional relationship between a boring tool and one or more buried lines such as, for example, pipes, cables, conduits or other conductors and more particularly to an arrangement for indicating certain changes in the positional relationship between the boring tool and the lines based upon a particular characteristic of a magnetic field emanated from the boring tool or a magnetic field emanated from each one of the lines. In one aspect of the invention, an arrangement and associated method are provided for tracking the positional relationship between a boring tool and one or more buried lines using a composite magnetic signal.
The installation of utility lines underground is increasingly popular for reasons of aesthetics and for practical reasons such as, for example, protecting these lines from the effects of severe above ground weather conditions. However, in areas where buried lines have previously been installed, it is undesirable to excavate an entire pathway for the purpose of installing additional lines since such excavation many times results in the unintentional damage of an existing utility line. Areas which include buried fiber optic cables are particularly problematic for several reasons. First, a fiber optic cable is extremely difficult to repair once it has been severed or damaged. Second, because a fiber optic cable is capable of simultaneously carrying a vast amount of information, downtime can be quite costly.
In the past, various horizontal boring tool locating and monitoring systems have been developed which advantageously eliminate the need for excavating the entire pathway in which a utility line is to be installed. One such system is described in U.S. Pat. No. 5,337,002 (issued to the inventor of the present invention) which is incorporated herein by reference. FIG. 1 is taken directly from the ""002 patent and illustrates a horizontal boring operation being performed by an apparatus which is generally designated by the reference numeral 10. Boring apparatus 10 includes a drill head 12 incorporating a transmitter which transmits a locating signal 14. A portable hand held receiver (locator) 16 is used to detect the locating signal through the intervening earth whereby to ultimately guide the boring tool to a terminating pit 18. The system relies on its operator having prior knowledge of any obstacles in the boring path of the tool such as an obstacle 20 so that the tool can be steered around the obstacle. Unfortunately, such prior knowledge may be inaccurate, if available at all. Moreover, the system of FIG. 1 does not by itself provide a direct indication of the relationship between a respective obstacle such as an in-ground line and the boring tool. Without this indication, the operator is in danger of possibly damaging an in-ground line with no forewarning. In view of the serious consequences of damaging certain buried lines, as described above, operators of boring tools are less and less willing to assume this risk.
As will be seen hereinafter, the present invention provides a highly advantageous arrangement and associated method for providing an operator with indications which warn the operator when a boring tool is approaching an in-ground obstacle such as a fiber optic cable. Dependent upon the specific indications provided to the operator, an appropriate course of action may thereafter be taken which assures that the boring tool will not damage the line. In another advantage, the present invention provides an arrangement which utilizes a composite magnetic signal in determining both the directional heading of the boring tool and the positional relationship between the boring tool and the underground line(s). The arrangement may be configured so as to enable simultaneous tracking of the positional relationship between the boring tool and a plurality of in-ground lines whereby to avoid physical contact of the boring tool with the lines.
As will be described in more detail hereinafter, there is disclosed herein a system in which a boring tool is moved through the ground in a region which includes at least one electrically conductive in-ground line. The system, like the system of FIG. 1, includes a boring tool. However, the system of the present invention includes an arrangement for tracking a specific positional relationship between the boring tool and one or more in-ground lines. The arrangement includes first means for generating a magnetic field from one of either the boring tool or the line. Second means for detecting a particular characteristic of the generated field is carried by the boring tool if the field is generated from the line or is connected to the line if the field is generated from the boring tool. The characteristic varies as a function of the specific positional relationship between the boring tool and the line as the boring tool moves through the ground within the region. Third means is included which is responsive to the detection of the characteristic for indicating certain changes in the positional relationship between the boring tool and each one of the lines being monitored.
In one aspect of the present invention, a boring tool is moved through the ground in a region which includes at least one electrically conductive in-ground line and which is subject to static magnetic fields including the magnetic field of the earth. Tracking a positional relationship between the boring tool and the line, as well as determining a directional heading of the boring tool within the region are provided by: (i) generating a time varying magnetic field from the line; (ii) at the boring tool, detecting a composite magnetic signal which includes one component affected by the static magnetic fields and another component affected by the time varying magnetic field such that the static magnetic field component varies as a function of the directional heading and the time varying component varies as a function of the positional relationship; and (iii) processing the composite magnetic signal to separate the static magnetic field component and the time varying magnetic field component from the composite magnetic signal for use in determining the directional heading and the positional relationship. In one feature, the static magnetic field component is used to determine the directional heading of the boring tool and the time varying magnetic field component is used to determine the positional relationship.